Orals: Mon, 4 May, 08:30–10:15 | Room 0.31/32
Astronomical insolation curves calculated for the top of Earth’s atmosphere show that the variations in (summer) insolation received at low and intermediate latitudes are dominated by (eccentricity-modulated) precession, while obliquity becomes important only at high latitudes. Nonetheless, empirical and modelling studies have shown that obliquity can exert a significant control on lower-latitude (paleo)climate, via its influence on cross-equatorial/meridional temperature gradients or the equatorward transfer of high-latitude (e.g. glacial) signals. Here we explore the origin of regular mudstone-carbonate alternations within the Mesoproterozoic Hakatai Shale of the Grand Canyon, whose cyclostratigraphy points to the combined influence of climatic precession and obliquity forcing on an ancient sabkha-playa system that was situated at subtropical paleolatitudes. We also present new age constraints for the Hakatai based on CA-ID-TIMS U-Pb zircon dating. The results of lithofacies, major and trace element analysis and a lateral stratigraphic correlation of the patterns across 65 km (from Tapeats Creek to Red Canyon) reveal a stronger contribution of obliquity relative to precession at the more landward (continental) vs shoreward sites. We hypothesize that this change in obliquity power over a relatively short distance is explained by a stronger sensitivity (and nonlinear response) to obliquity-paced sea level variations, which determined the supply of marine alkalinity to the coastal mudflat and the formation of carbonate-rich beds in addition to precession, influencing regional paleohydrology, in situ carbonate production/precipitation and storm supply. Variations in high-latitude (continental) ice volume and low-latitude monsoonal circulation may thus both have been operative during the early assembly phase of Rodinia in response to astronomical-induced insolation changes.
How to cite: Lantink, M., Eyster, A., Davies, J., Kocken, I., Meyers, S., Perrot, M., and Segessenman, D.: On the origin of precession and obliquity cycles within the Mesoproterozoic Hakatai Shale (Grand Canyon), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21535, https://doi.org/10.5194/egusphere-egu26-21535, 2026.
The Alum Shale Formation of Baltica preserves one of the most continuous and fossil-rich records of the Cambrian, making it a key sedimentary archive for refining global chronostratigraphy, reconstructing carbon cycle perturbations, and assessing astronomical forcing on high-latitude systems during an early Palaeozoic greenhouse world. A high-resolution cyclostratigraphic and multiproxy study of the middle Cambrian succession from the Albjära-1 drill core (southern Sweden) establishes a 173 kyr obliquity-tuned astronomical time scale (ATS), anchored by a high-precision U–Pb age. Integration of this time scale with new carbon isotope data and refined biostratigraphy places the Albjära-1 core as a global reference record. This framework provides the first numerically constrained ages and durations for the Drumian Carbon Isotope Excursion (DICE), enabling worldwide synchronization of biostratigraphy and carbon cycle events. Coupled elemental geochemistry and time calibration reveal that obliquity- and eccentricity-driven climate oscillations modulated sea-level and dust fluxes governing middle Cambrian outer-shelf sedimentation at high-latitudes. These results highlight the sensitivity of Earth’s early Paleozoic greenhouse systems to astronomical forcing.
How to cite: Jamart, V., Hinnov, L. A., Spangenberg, J. E., Adatte, T., Nielsen, A. T., Schovsbo, N. H., Thibault, N., Arts, M., Daley, A. C., and Pas, D.: Astronomical calibration of the middle Cambrian in Baltica: Global carbon cycle synchronization and climate dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-510, https://doi.org/10.5194/egusphere-egu26-510, 2026.
The International Continental Scientific Drilling Program of the Songliao Basin has obtained continuous cores and abundant well logs from the Lower Cretaceous Shahezi Formation. This provides a valuable archive for understanding terrestrial paleoenvironmental and paleoclimatic changes during the Early Cretaceous. Based on lithological data and well logs, we conducted a study of paleoclimatic cycles within the Shahezi Formation. The results indicate that lithological curves and various well logs from the Shahezi Formation record orbital-scale climatic cycles. Spectral analysis of the tuned lithological curves reveals the millennial-scale cycles in the lower part of the Shahezi Formation. The results of filtering the tuned lithological curves show that the extracted eccentricity and precession curves exhibit good consistency with the amplitude variations of the millennial-scale cycles. This may suggest that millennial-scale climate variability recorded in the Shahezi Formation is driven or modulated by orbital-scale climatic forcing. This study is helpful for understanding the response of terrestrial environment to climate change in Early Cretaceous.
How to cite: Peng, C. and Zou, C.: Orbital- and millennial-scale climate changes in terrestrial Early Cretaceous sedimentary strata from the International Continental Scientific Drilling Program of the Songliao Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17033, https://doi.org/10.5194/egusphere-egu26-17033, 2026.
Multimillion-year proxy records across the Eocene show prominent variations on orbital time scales. The cycles, which have been identified at numerous sites across the globe, preferentially concentrate spectral power at eccentricity and precessional frequencies. It is evident that these cycles are an expression of changes in global climate and carbon cycling paced by astronomical forcing. Importantly, there is robust evidence that orbital forcing is also the pacemaker for a long sequence of transient Eocene climate events, called hyperthermals. Little is known though about the link between orbital forcing and the carbon cycle-climate system. Here I will analyze climate and carbon cycling changes across the Eocene hyperthermals in relation to astronomical forcing using a variety of proxies. Furthermore, I will apply the analysis to the largest hyperthermal event throughout the Cenozoic, the Paleocene-Eocene Thermal Maximum (PETM, 56 Ma). The PETM was associated with about 5 K global surface warming and an estimated total carbon release of several thousand Pg, rendering the PETM an event that is widely considered the best analog for present/future carbon release. Next, I will compare the Eocene hyperthermals and the PETM, pointing out commonalities in their response to orbital forcing. Moreover, carbon vs. oxygen isotope excursions show very similar slopes during the hyperthermals, as well as the PETM, pointing to a common origin. The results underline that the PETM is not an isolated event, but rather part of a sequence of early Cenozoic hyperthermals. I will also discuss the conundrum that the observed duration of the PETM appears to be much longer than predicted by models that use first order assumptions. Understanding the long duration of the PETM in relation to orbital forcing is also critical for predicting the long-term consequences of anthropogenic carbon release. In that context, I will identify a remarkable pattern in the forcing and response to the short eccentricity cycle and the duration/nature of the hyperthermals vs. the PETM.
How to cite: Zeebe, R.: Orbital forcing of the Eocene Hyperthermals and the Paleocene-Eocene Thermal Maximum, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13838, https://doi.org/10.5194/egusphere-egu26-13838, 2026.
Arid regions in the Northern Hemisphere significantly influence global terrestrial biogeography, yet systematic research on their orbital-to-millennial-scale aridity dynamics remains limited. Here, we analyze orbital-to-millennial-scale climate fluctuations using dust flux records from two marine sediment cores reflecting the evolution of the Sahara-Arabian Desert and two terrestrial sediment cores recording hydroclimate changes in Central Asia. Our results reveal that the expansion of Northern Hemisphere ice sheets and shifts in glacial boundary conditions (i.e. marine ice-sheet expansion) drive orbital-scale aridification climate variability through atmospheric-ocean circulation. Millennial-scale climate fluctuations in these regions are persistently influenced by changes in obliquity and eccentricity-modulated precession amplitude, further highlighting the regulatory role of high-latitude ice sheets and sea ice on millennial climate variability. A re-examination of existing fossil records from East Africa demonstrates that periods of shifts in the dominant climate cyclicity and changes in obliquity sensitivity of marine dust fluxes coincide temporally with the major stages of hominin evolution. This suggests that periods of instability in Earth's climate system were a critical trigger for hominin evolution.
How to cite: Wang, Z., Gao, Z., Zhang, Z., Zhang, R., Wu, Q., Wang, W., Wei, H., and Han, W.: Orbital and millennial-scale climate forcing of the Northern Hemisphere aridity and its influence on human evolution over the past 3.6 Myr, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2482, https://doi.org/10.5194/egusphere-egu26-2482, 2026.
The prolonged minimum in Antarctic δD and CO2 and extended interval of high benthic δ18O between 190 and 134 ka (MIS6) is often interpreted as a prolonged stable glacial period with ice sheets insensitive to the large amplitude precessional variations in high latitude insolation. Here, we evaluate the evidence for Northern Hemisphere (NH) ice sheet stability from indicators of North Atlantic surface ocean δ18O. Since the North Atlantic receives nearly all meltwater from NH ice sheets, its surface δ18O is highly sensitive to NH ice sheet mass balance. The δ18O from speleothems in coastal caves in NW Spain is dominantly driven by the surface ocean δ18O signal from a broad area of the North Atlantic Ocean which comprises the moisture source for rainfall above the caves. Here we present a new speleothem δ18O sequence from absolutely dated speleothem covering 216 to 111 ka. Our new speleothem δ18O shows evidence for large amplitude, precessionally-paced variations in the d18O of the North Atlantic. The magnitude of abrupt freshening during rising insolation at 183-178 ka is comparable to the positive δ18O shift marking ice buildup between 195-184 ka. A significant freshening also occurs during rising insolation at157-151 ka. Lower resolution δ18Osw records from the Southern Iberian Margin, derived from paired Mg/Ca and δ18O of planktic foraminifera G. bulloides, confirm these precessional cycles. The absolute speleothem chronology confirms that over all 4 examined precessional cycles, peak freshening occurs within a similar narrow range 65N summer insolation, but across a very broad range of 65N caloric summer insolation. The prolonged stable δ18O in benthic stacks, despite significant variation in NH ice sheets, may imply significant antiphased precessional variation in the Antarctic ice sheet. A more dynamic NH ice sheet history during MIS 6 also has implications for the GIA models used to infer sea level during the last interglacial.
How to cite: Stoll, H., Kost, O., Cheng, H., Cacho, I., Torner, J., and Jaggi, M.: Dynamic precessional forcing of NH ice sheets during MIS 6 , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5937, https://doi.org/10.5194/egusphere-egu26-5937, 2026.
The intensification of Northern Hemisphere Glaciation (iNHG, ~2.7-2.4 Ma) marks a major climatic shift from the relatively warm and stable mid-Pliocene climate to the high-amplitude glacial–interglacial cycles of the early Pleistocene. Recent geochemical evidence from IODP Site U1385 on the Iberian Margin suggests that the iNHG was also associated with the emergence of millennial climate variability (MCV), an intrinsic feature of Quaternary glacial periods. These millennial-scale cooling events (stadials) first appear as isolated precursor events since MIS G6 (~2.7 Ma), and recur as multiple events within glacials from MIS 100 (~2.5 Ma) onward. This stepwise evolution raises the question of how MCV, nested within glacial cycles, responds to orbital forcing and the evolving climate background state (e.g. long-term cooling and CO₂ decline). Here, we explore this using new high-resolution planktic and benthic foraminiferal oxygen isotope records and X-Ray Fluorescence (XRF)-derived Zr/Sr ratios from Site U1385, spanning ~3-1.8 Ma and encompassing the iNHG.
Orbital-phase analyses indicate that obliquity strongly governs the timing of glacial terminations and inceptions across the study interval. Precession, together with obliquity, modulates the rate of ice-volume change and the associated shapes of glacial cycles. Within glacial periods, MCV exhibits strongly state-dependent, threshold-like behaviour, with stadials preferentially occurring under lower obliquity and higher benthic δ18O values. The number of stadial events within individual glacial cycles appears to increase with both the duration and intensity of glacial periods beyond a benthic δ18O threshold, and is further modulated by the magnitude of the corresponding obliquity minimum. Together, these results suggest that sufficiently intense and long-lived glacials provide the background conditions under which multiple stadial events can be sustained, thereby offering a conceptual basis for the observed MIS G6-100 shift from isolated precursors to persistent millennial-scale oscillations. This pattern is consistent with the development of marine-terminating ice-sheet margins as Northern Hemisphere glaciation intensified, potentially enabling iceberg calving and associated MCV to persist from MIS 100 onward.
How to cite: Du, M., Crowhurst, S. J., Mleneck-Vautravers, M. J., Rolfe, J. E., and Hodell, D. A.: Threshold Response of Millennial Climate Variability to Orbital Forcing and Glacial Boundary Conditions Across the Intensification of Northern Hemisphere Glaciation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5233, https://doi.org/10.5194/egusphere-egu26-5233, 2026.
The western equatorial Pacific (WEP) plays an important role on global climate. Many studies have reported the classical orbital cycles in the WEP temperature variations, but the half-precession (~10-kyr) cycle, despite its uniqueness in the equatorial insolation, is paid less attention. Here, a systematic study on the half-precession cycle in the WEP temperature is performed based on the analysis of transient climate simulations covering the past 800,000 years, combined with high-resolution temperature reconstructions. The results show that the half-precession cycle is a significant signal in the WEP temperature. The model simulations show that in response to astronomical forcing, the half-precession cycle in the WEP surface and upper subsurface temperatures is driven by maximum equatorial insolation, while it is driven by bi-hemisphere maximum insolation in the lower subsurface temperature. The different forcing mechanisms at different depths are related to distinct local ocean circulation patterns. The astronomically-induced half-precession cycles are modulated by eccentricity, CO2 and ice sheets. Given the importance of WEP on global climate, the half-precession cycle in the WEP temperature may contribute to the half-precession signal recorded in other regions.
How to cite: Wu, Z., Yin, Q., André, B., and Guo, Z.: Forcing mechanisms of the half-precession cycle in the western equatorial Pacific temperature, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5994, https://doi.org/10.5194/egusphere-egu26-5994, 2026.
The Arabian Peninsula experienced pronounced hydroclimate shifts during the last 20,000 years, driven by orbitally forced changes in insolation that modulated monsoon strength, ITCZ position, and large-scale atmospheric circulation across distinct climate regimes. Using the LOVECLIM Earth system model, we reconstruct temperature and precipitation evolution across northern, central, and southern Arabia from the Last Glacial Maximum to the present, and evaluate the underlying mechanisms using orbital parameters and associated changes in tropical–extratropical circulation. The simulations reproduce key features observed in regional proxy archives, including early Holocene humid conditions, the 8.2 ka monsoon weakening, mid-Holocene aridification, and the establishment of modern desert climates after 4 ka BP. Precession emerges as the dominant control on monsoon intensity and rainfall in central and southern Arabia, whereas obliquity exerts the strongest influence in northern Arabia by modulating meridional temperature gradients and the poleward extent of monsoon penetration. Eccentricity acts as a low-frequency amplifier of precessional forcing, shaping the pacing and amplitude of humid–arid cycles. The modeled ITCZ position shows a major northward shift to approximately 25–28°N during the early Holocene, consistent with enhanced monsoon penetration, followed by a progressive southward retreat through the mid- to late Holocene. These results demonstrate that Arabia lies at the intersection of tropical and extratropical forcing regimes, where the interaction between precession-driven monsoon dynamics and obliquity-driven circulation changes governs spatially heterogeneous hydroclimate responses. This study provides an integrated framework for interpreting regional proxy records and highlights the mechanisms linking astronomical forcing to long-term hydroclimate evolution in the Arabian Peninsula.
How to cite: Alsarraf, H. and Kokkalis, P.: Orbital Forcing of Arabian Peninsula Hydroclimate from the Last Glacial to Present, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5128, https://doi.org/10.5194/egusphere-egu26-5128, 2026.
The Tropical Western Pacific Warm Pool (WPWP) constitutes a core component of the global climate system. Acting as a major reservoir of heat and moisture, it has a significant impact on the redistribution of energy between the ocean and the atmosphere. It is a key region in the global climate system. Variations in sea surface temperature and salinity, precipitation, and oceanic currents across the WPWP exhibit a pronounced semi-annual cycle driven by insolation, latitudinal migration of the Intertropical Convergence Zone (ITCZ), the monsoon system, and the coupled ocean–atmosphere interactions. Recent studies show that this semi-annual variability is modulated by climate oscillations, such as El Nino Southern Oscillation or Indian Ocean Dipole, and may vary over longer periods of time. Here, we provide evidence for modern to mid-Holocene variations in the semi-annual cycle from both proxy data and transient model experiments. Geochemical and sclerochronological records were derived from modern and fossil of giant clam shells (Tridacna spp.) collected from Belitung Island, in the middle of the Karimata Strait in Indonesia. Monthly to daily resolved proxy data is compared to 5 coupled transient simulation models for the Holocene: EC-Earth, AWI-ESM2, MPI-ESM, ISPL-CM5 and IPSL-CM6. Stable isotopes (δ¹⁸O, δ¹³C) from the shells provide reconstructions of sea surface conditions of past environmental conditions. The modern results from the shells are consistent with the measured modern data, supporting the use of giant clam as a proxy for past reconstructions. Model simulations suggest that the structure of the seasonal cycle in the WPWP varied during the Holocene compared to today, driven by orbital forcing of the insolation and internal climate feedbacks. Comparisons across models reveal that they do not converge on the exact magnitude and timing of cold/warm phases but all show warmer and wetter conditions in the second half of the Holocene. Holocene proxy data from the Karimata Strait also show changes in both the amplitude and the structure of this semi-annual variability. Results show an increase in the amplitude of the semi-annual compared to the seasonal cycle during the Holocene. The comparison with transient models highlights an overestimation of variations by the models, which we propose may be related to salinity. Furthermore, the IPSL and EC-Earth models agree with proxy data concerning the amplification of the semi-annual cycle relative to the seasonal cycle. This multi-proxy model data comparison approach based on Tridacna shells offers new insights into the evolution of seasonal and semi-annual variability in the WPWP from today to the mid-Holocene and a better understanding of the forcing mechanisms.
How to cite: Boutreux, C., Elliot, M., Carré, M., Abdelkader Di Carlo, I., Schöne, B. R., Braconnot, P., and Cahyarini, S. Y.: Coupling at semi-annual timescale of ocean-atmosphere processes in the Tropical Western Pacific Warm Pool during the Holocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18145, https://doi.org/10.5194/egusphere-egu26-18145, 2026.
Cyclostratigraphy relies on spectral analysis to decode the imprint of astronomical cycles in stratigraphic proxy data. Traditional methods, such as Fourier-based techniques and the continuous wavelet transform (CWT), are constrained by a fundamental trade-off between temporal and frequency resolution. These limitations constrain the ability of these spectral techniques to track changes in astronomical periods with stratigraphic depth and to separate cycles with closely spaced frequencies simultaneously. The recently developed superlet transform overcomes these classical limitations by combining multiple wavelets at the same central frequency, each with a different number of cycles controlling its Gaussian envelope width. By computing the geometric mean of the wavelet responses, superlets achieve enhanced frequency resolution while maintaining temporal precision, yielding a sharper time–frequency representation than the conventional CWT. Here, we present a new suite of functions in the WaverideR R package that applies the superlet transform to cyclostratigraphic datasets. The implementation is specifically tailored to the characteristics of (cyclo)stratigraphic proxy records, incorporates log2-period scaling, supports analysis in both the depth and time domains, and employs FFT-based convolution to improve computational efficiency. Using these tools, users can generate superlet scalograms, identify and track the periods of astronomical cycles, and construct cyclostratigraphic age models. The superlet transform also enables the study of amplitude-modulation patterns and the discrimination of closely spaced cycles, such as those comprising short eccentricity or precession signals, a task that the classical CWT struggles with. Tests on both synthetic and real stratigraphic datasets demonstrate that the superlet transform substantially improves spectral fidelity compared to traditional wavelet- and Fourier-based methods, establishing it as a powerful tool for analysing and interpreting astronomical signals in proxy records.
How to cite: Arts, M., Huygh, J. J. C., and Da Silva, A.-C.: Enhancing spectral fidelity in cyclostratigraphic studies using superlets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17093, https://doi.org/10.5194/egusphere-egu26-17093, 2026.
Cyclostratigraphic methods provide an effective framework for resolving temporal organization and stratigraphic architecture in sedimentary systems affected by complex depositional processes. In this study, spectral analysis of gamma-ray logs from two wells (A and B) drilled into Cretaceous pre-salt carbonate reservoirs of the Santos Basin, offshore Brazil, is used to investigate orbital-scale sedimentary cyclicity. The objective is to improve temporal resolution and to evaluate the implications of astronomically forced signals for reservoir characterization and exploration-focused stratigraphic models. Well-defined orbital signals are identified, characterized by persistent cyclicities between ~21 and 28 m and statistically significant spectral peaks above the 95% confidence level. These cycles are interpreted as expressions of the long-eccentricity (405 kyr) orbital cycle. Eight 405 kyr cycles are recognized in well A, whereas seven cycles are identified in well B, corresponding to time intervals of ~3.2 Myr and ~2.8 Myr, with average sedimentation rates of ~6.7 cm/kyr and ~9.05 cm/kyr, respectively. Independent sedimentation rate estimates derived from the TimeOpt method (~6–8 cm/kyr) support these results, while comparison with evolutionary harmonic analysis (EHA) reveals a stable low-frequency spectral pattern throughout the studied interval. The persistence of these cycles across different lithologies highlights the dominant role of astronomical forcing on sedimentation processes, even within complex carbonate systems. In addition, maxima in long-eccentricity cycles are systematically associated with maximum regressive surfaces. These findings demonstrate the value of cyclostratigraphy as a robust tool for refining stratigraphic correlations in pre-salt carbonate reservoirs, constraining sedimentation rates, improving chronostratigraphic frameworks, and supporting reservoir development and future exploration strategies.
How to cite: Leandro, C., Savian, J., Tedeschi, L., and de Moura, D.: Orbital Pacing of Sedimentation and Reservoir Architecture in Pre-Salt Carbonates, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15496, https://doi.org/10.5194/egusphere-egu26-15496, 2026.
The Carnian Pluvial Episode (CPE; 234–232 million years ago) is an iconic but poorly understood hyperthermal event. Here, we present an integrated high resolution (~2–10 kyr) multi-proxy record from a Carnian lacustrine succession of the Junggar Basin of northwestern China. The high-resolution palaeontological, sedimentological and geochemical signals from the Dalongkou section enable the precise identification of the onset of the CPE and enhanced volcanic activity, supporting the interpretation that the rapid onset of the CPE (~15.8 kyr) could have been the result of volcanism and subsequent surface carbon-cycle feedbacks.
We employ cyclostratigraphic (magnetic susceptibility) and organic-carbon isotopic data to explore the carbon-cycle dynamics. The Earth’s orbital eccentricity periodicity originates from the beat frequencies between the secular fundamental frequencies of the perihelion precession. The (𝑔2−𝑔5) 405-kyr cycle, which mainly involves the fundamental frequencies of Venus and Jupiter, is the most stable term in a quasi-periodic approximation of the Earth’s orbital parameter. Based on the 405-kyr tuning scheme and the modulation analysis of short eccentricity terms, the CPE terrestrial carbon cycling, at a scale of ± 1‰ (δ13Corg), displays an in-phase relationship with the 405-kyr-long-eccentricity oscillation, i.e., the higher values of the δ13Corg are correlated with high eccentricity (high variance of precession), and vice versa. This relationship suggests that during eccentricity minima, cooler and more stable climates, within a generally warm background, facilitated the expansion of continental carbon reservoirs. This expansion led to greater land storage of isotopically light carbon and a corresponding rise in marine dissolved inorganic carbon (δ¹³C-DIC), with the reverse occurring during maxima. This in-phase behavior is most pronounced in the CPE interval because the 405-kyr eccentricity-related forcing signal was amplified by internal climate feedbacks of the carbon cycle under hyperthermal conditions. This result, together with previous long-term carbon isotope records, shows that such a climate–carbon-cycle interaction may have been widespread throughout the warm Mesozoic Era, including hyperthermal intervals.
In addition, we investigate the global changes in hydrological cycling during the CPE using a combination of palynological and sedimentological data, as well as Earth System modelling. Together, these data allow a comprehensive overview of climate–carbon-cycle dynamics, including potential driving mechanisms for the CPE, and coeval changes to the hydrological cycle. The CPE hydrological cycle was typified by increased aridification in continental interiors and multiple precipitation centers at low-latitude eastern regions of Pangea and at the poles. The carbon and hydrological cycle changes of the CPE include features reminiscent of other warm events, suggesting they may share key characteristics and hold important clues to Earth system functioning.
How to cite: Xue, N., Zhao, X., Yang, H., De Vleeschouwer, D., Wang, B., and Claeys, P.: Orbitally paced climate–carbon-cycle interactions and spatial heterogeneity of the late Triassic Carnian pluvial episode, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3163, https://doi.org/10.5194/egusphere-egu26-3163, 2026.
The Earth’s ancient astronomical parameters are derived from high-fidelity cyclostratigraphic records in which observed cycles are dominantly controlled by two sets of factors: (1) orbital parameters involving the orbital motions of the planets, and (2) rotational parameters involving Earth’s spin, lunar separation and precession rate. A full astronomical solution (AS) for the Earth is thus comprised of an orbital solution (OS) and a precession solution (PS) [1].The OS is constrained to 0-60 Ma [2]; prior to 60 Ma chaotic behavior of planetary orbits results in a non-unique OS. The PS is constrained by geophysical modeling of dynamical ellipticity (De) and tidal dissipation (Td) [3, 4].
For times prior to 60 Ma, recovery of the AS relies on cyclostratigraphy. OS ZB18a and PS ZB18a(De=1,Td=0.9) have been proposed as candidates for a 58-66 Ma AS from ODP Site 1262 cyclostratigraphy [5], and OS (ZB20a) for a 66-71 Ma AS from Zumaia (Spain) cyclostratigraphy [6]. Here we examine an extension of Site 1262 cyclostratigraphy from the Cretaceous-Paleogene Boundary (KPB; 66 Ma) reaching back ~1 million years into the Late Maastrichtian [7]. The goal is to test the fit of various available OS (e.g., ZB20a, ZB18a) with cyclostratigraphy for this interval, and whether PS parameters appear to be consistent with post-KPB PS parameter values of De=1 and Td=0.9.
The sequence of XRF Core Scanner Fe area counts for Site 1262 (216.74-236.02 rmcd) was analyzed with TimeOpt [8] and AstroGeoFit [9]. TimeOpt identified a constant sedimentation rate of 2.13 cm/kyr, and constrained spectral power in two narrow-band lines consistent with short orbital eccentricity, and elevated power across the precession band. TimeOpt with a linearly increasing sedimentation rate template reorganized precession band power into four narrow-band lines consistent with precession frequencies. A close examination hinted that other variable sedimentation rates along the sequence remained undiscovered. AstroGeoFit confirmed the linear increase in sedimentation rate, and identified additional fluctuations that reorganized power into specific precession line frequencies.
The TimeOpt results indicate a close match between late Maastrichtian Site 1262 and OS ZB18a and PS ZB18a(De=1,Td=0.9), as was found previously for the post-KPB interval (58-66 Ma) [5]. The AstroGeoFit results improve on this finding. Finally, a KPB geochronologic anchor of 66.021 ± 0.024/0.039/0.081 Ma [10] for Site 1262 guides the assignment of an absolute timescale and precession-scale astrochronology for Site 1262.
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How to cite: Brisson, M., Omar, H., Segessenman, D., and Hinnov, L. A.: Seeking an accurate astronomical solution from ~66-67 Ma Cretaceous-Paleogene boundary-interval cyclostratigraphy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14209, https://doi.org/10.5194/egusphere-egu26-14209, 2026.
In the modern ocean, deep-water formation does not occur in the North Pacific. Yet, geological evidence suggests that ocean circulation during past warmhouse climates may have differed fundamentally from today. The Early Eocene, characterized by elevated greenhouse gas concentrations and strong orbital pacing, provides a key test case for exploring alternative modes of deep-ocean ventilation. However, the extent to which individual orbital parameters modulated deep-water formation in the North Pacific remains poorly understood.
Here, we use the intermediate-complexity Earth system model cGENIE to perform a suite of orbital sensitivity experiments under the Early Eocene climate boundary conditions, systematically isolating the effects of eccentricity, obliquity and precession on ocean circulation. By holding background climate boundary conditions constant, our experiments allow direct assessment of the dynamical response of the ocean to orbital forcing alone.
The simulations reveal that precession exerts a substantially stronger control on ocean circulation strength than either eccentricity or obliquity, with the most pronounced response occurring in the North Pacific. Under precession minimum configurations, reduced summer insolation leads to cooler surface waters and enhanced winter buoyancy loss. This promotes deeper winter mixed layer, increases vertical exchange, and enables sustained deep-water formation in the North Pacific. In contrast, precession maximum configurations are associated with warmer surface waters and weaker winter cooling, limiting mixed-layer deepening and favoring the formation of intermediate rather than deep waters.
Our findings highlight precession as a key regulator of deep-water formation in ice-free climates and demonstrate that changes in seasonal insolation can trigger major reorganization of ocean circulation. This provides new mechanistic insight into how orbital forcing may have contributed to variability in ocean ventilation, carbon cycling, and climate stability during past greenhouse worlds.
How to cite: Jiang, Q., Li, M., Papadomanolaki, N. M., and De Vleeschouwer, D.: Turning the North Pacific Over: Earth System Model Experiments Reveal Precession-Driven Deep-Water Formation in the Early Eocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3324, https://doi.org/10.5194/egusphere-egu26-3324, 2026.
Milankovitch cycles in paleoclimate records demonstrate that astronomical forcing has impacted Earth’s climate-carbon dynamics throughout Earth’s history. Its influence is especially pronounced during warmer intervals like the Early Eocene Climatic Optimum during which periodic carbon release events, or ‘hyperthermals’, occurred at a pacing consistent with eccentricity. Yet, the reservoirs and mechanisms responsible for orbitally driven carbon release-sequestration are poorly understood. With the cGENIE Earth system model, we pick apart how different components of the Earth system respond to insolation forcing. Detailed evaluation of marine carbon cycle feedbacks has demonstrated that organic carbon and nutrient cycling can greatly amplify orbital climate and CO2 variability but results also hint at important missing feedback processes, possibly of terrestrial origin. Here, I present ongoing model development to include a terrestrial scheme in our model. I show preliminary results of how vegetation growth and soil carbon storage change with orbital forcing and their feedback on climate and atmospheric CO2. Importantly, I will also address land-ocean interaction and evaluate how orbitally driven changes to the surface dynamics and terrestrial carbon storage impact ocean circulation and biogeochemistry. Ultimately, our research will reveal what reservoirs and processes are most sensitive to orbital forcing and can be used to guide hypotheses for orbitally driven triggers of larger-scale events.
How to cite: Vervoort, P., Greene, S. E., and Kirtland Turner, S.: Modelling the response and impacts of terrestrial feedbacks to orbital forcing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18073, https://doi.org/10.5194/egusphere-egu26-18073, 2026.
In Milanković theory, changes in the Earth’s obliquity and climatic precession combine to pace the growth and decay of Northern Hemisphere ice sheets by controlling summer insolation at the high northern latitudes. However, in the glacial-interglacial cycles of the Early Pleistocene, the strength of the obliquity cycle consistently outweighs precession, despite the fact that precession strongly controls the intensity of summer insolation. Consequently, the dominance of the obliquity cycle during the ‘41-kyr world’ of the Early Pleistocene has been referred to as Milanković’s other unsolved mystery. In this study, we present simulations of a zonally-averaged energy balance model (ZEMBA) in response to these orbital cycles. Transient simulations spanning the Early Pleistocene (from 2.4 to 1.2 Ma) show a pronounced 41-kyr obliquity cyclicity in polar temperature similar to the paleoclimate records. Further sensitivity experiments underscore the importance of obliquity over precession, and of sea ice over snow cover, in driving this polar temperature variability. We present new results that attribute the prevalence of the 41-kyr obliquity cycles in ZEMBA to the influence of the orbital parameter on winter sea ice, which regulates the release of large stores of ocean heat to the atmosphere. In contrast, the muted effect of precession on surface air temperature arises from the counterbalancing relationship between insolation intensity and summertime duration, limiting its influence on winter sea ice extent and thereby temperature variability.
How to cite: Gunning, D., Nisancioglu, K., van de Wal, R., and Capron, E.: On the Dominance of Obliquity in the Early Pleistocene Glacial Cycles: Insights from an Energy-Balance Climate Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14328, https://doi.org/10.5194/egusphere-egu26-14328, 2026.
The Pliocene (5.33-2.58 Ma) was comparatively warmer (+ 1.8-3.6 0C) than today and was characterized by elevated CO2 concentrations (400 ppmv). Thus, studying sedimentary sequences dated to this interval can serve as excellent analogues for comparing present conditions and provide tools for better modeling future trends. Yet, while most studies rely on marine archives, continental data dating back to this interval are scarce, particularly from boundary regions such as the Levantine Corridor. Sediments from the Erk-el-Ahmar Fm. (lacustrine, 3.9 Ma, Jordan Valley, Israel) and Bnot Lot member of the Sedom Fm. (lagoonal/lacustrine, 3.2-4.0 Ma, Dead Sea, Israel) highlight as one of the few well-exposed continental archives in the region that date back to that time.
In the present contribution, we explore these two sedimentary archives and integrate in a multi-proxy fashion the physical, chemical, and biological properties of both outcrop and core sections (with the latter only retrieved from the Erk-el-Ahmar sequence). This study aims to reconstruct the paleoenvironmental setting and changing hydroclimatic conditions in the Levantine Corridor during these time intervals. By amalgamating the datasets, we show that while the region is characterized by increased warmth and augmentation in precipitation patterns, occasional cooling phases coupled with drought punctuate the Pliocene climatic history in the Levantine region.
By synthesizing these diverse datasets into a consistent narrative, the project illuminates how precipitation, evaporation, and ecosystem processes interact under high-CO2 and high-temperature conditions. The outcomes provide the first robust benchmark of Pliocene hydroclimate evolution in the Levantine Corridor, offering critical insight into thresholds of lake resilience, feedback mechanisms, and the persistence of aquatic systems under sustained global warmth.
How to cite: Waldmann, N., Yunfa, M., Olaopa, O., Danish, M., Niu, G., Greenlee, J., Parth, S., Mazzini, I., Castañeda, I., and Taha, N.: Sharp turnovers in Pliocene hydroclimate variability in the Levantine Corridor, East Mediterranean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17979, https://doi.org/10.5194/egusphere-egu26-17979, 2026.
Posters virtual: Fri, 8 May, 14:00–18:00 | vPoster spot 4
EGU26-7110 | ECS | Posters virtual | VPS7
Orbital eccentricity pacing of hydroclimate variability in Qinghai-Tibet Plateau during the middle–late EoceneFri, 08 May, 14:06–14:09 (CEST) vPoster spot 4
The middle–late Eocene climate evolution and its orbital forcing mechanisms remain poorly constrained for Qinghai-Tibet Plateau. We present a radiometrically anchored astrochronological framework and orbital-scale hydroclimate reconstruction from the Niubao Formation in central Tibet, spanning the interval between the Middle Eocene Climatic Optimum (MECO) and the Eocene–Oligocene Transition (EOT). A key tuff bed yields a zircon U–Pb age of 36.50±0.21 Ma, providing an independent tie point for stratigraphic calibration and sedimentation rate assessment. High-resolution elemental geochemistry and carbon isotope stratigraphy were analyzed using MTM spectral methods and cyclostratigraphic approaches. Proxy ratios sensitive to aridity/humidity (Sr/Cu, Al/Mg, K/Al, Sr/Ba), weathering and hydrology (Rb/Sr, Ti/K), and redox conditions (Fe/Mn) display persistent orbital pacing, with dominant periodicities at 405 kyr and 100 kyr, consistent with long and short eccentricity forcing. Across the studied interval we observe an overall trend toward more arid conditions, while eccentricity-band variability modulates hydroclimate and redox states. Carbon isotope variations facilitate correlation to coeval global records, linking central Tibetan environmental change to global Eocene climate transitions.
How to cite: Pan, G. and Fu, X.: Orbital eccentricity pacing of hydroclimate variability in Qinghai-Tibet Plateau during the middle–late Eocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7110, https://doi.org/10.5194/egusphere-egu26-7110, 2026.
EGU26-8903 | ECS | Posters virtual | VPS7
Astronomically Driven Climate Change as an Amplifier of Carbon Cycle Instability and Ecological Crisis at the Norian-Rhaetian BoundaryFri, 08 May, 14:48–14:51 (CEST) vPoster spot 4
The Norian-Rhaetian boundary (NRB) marks a critical interval of Late Triassic global environmental instability, ecological crisis, and climatic transition, which preceded the sustained biodiversity decline culminating in the end-Triassic mass extinction. Despite its significance, the drivers of carbon cycle and biotic disturbances across the NRB remain unresolved. In most cases, these major mass extinctions in geological history are interpreted as chain reactions triggered by volcanic activity. Interestingly, the NRB and Rhaetian intervals lack compelling evidence for synchronous, precisely dated, large-scale volcanism with demonstrable global effects. In this context, the Central Atlantic Magmatic Province (CAMP) erupted later at ca. 201 Ma, while other impact-related triggers and/or proposed large igneous provinces (LIP), such as the Angayucham LIP in Alaska (214 ± 7 Ma), remained weakly constrained in magmatic timing, magnitude, and environmental significance. In the absence of significant volcanism, the mechanisms underlying carbon cycle perturbations and ecological crises become even more enigmatic.
Here, we present a high-resolution carbonate carbon isotope (δ13Ccarb) profile spanning the Late Triassic to Early Jurassic from South China. Through independent U-Pb dating and cyclostratigraphic analysis, a high-precision astronomical timescale was established. Carbon isotope variations are strongly controlled by orbital cycles, and the record reveals two large-magnitude negative carbon isotope excursions (CIEs) at ca. 205 Ma and 201 Ma, corresponding to the NRB and Triassic-Jurassic Boundary (TJB), respectively. Our study posits that astronomically driven climate change persistently influenced the NRB and subsequent Rhaetian intervals, triggering a series of chain reactions involving climate, vegetation, carbon burial, greenhouse gas emissions, and other factors. Ultimately, it acted as an amplifier in the NRB event, leading to carbon cycle perturbations and ecological crises during this period, thus potentially preconditioning the Earth system for the subsequent end-Triassic mass extinction. This study further highlights the significance of low-latitude coastal areas as dynamic amplifiers of carbon cycle instability and underscores the vulnerability of modern carbon reservoirs under ongoing climate change.
How to cite: Lu, T. and Fu, X.: Astronomically Driven Climate Change as an Amplifier of Carbon Cycle Instability and Ecological Crisis at the Norian-Rhaetian Boundary, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8903, https://doi.org/10.5194/egusphere-egu26-8903, 2026.
